Regular use of fish oil supplements and course of cardiovascular diseases: prospective cohort study.

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Fish oil supplements may have different effects for different people and medications may modify their effects. Care should be taken around regular use, and preferably under the guidance of a registered nutrition practitioner.

Introduction

The primary aim of this study was to assess associations between regular use of fish oil supplements and cardiovascular disease (CVD) outcomes and events in people with no known CVD. People at high risk of CVD were included. A secondary aim was to examine the modifying effects of fish oil supplements in people with known CVD for disease progression.

Methods

• Participants from the UK Biobank n=415,737 without known CVD, were followed up over a median period of 11.9 years. All participants were UK inhabitants aged 40-69 years at recruitment. N=130,365 (31.4%) self-reported as regular fish oil users at baseline.
• 6 transitional phases were monitored for disease progression from a healthy state to death including atrial fibrillation, myocardial infarction, stroke, heart failure, and major adverse cardiovascular events.
• Adjustments were made for the following covariates recorded at baseline; age, sex, ethnic group, obesity, hypertension, diabetes, use of specific medications, chronic pulmonary disease, chronic renal failure, and diet and fish consumption (oily and non-oily), alcohol intake and smoking status.

Results

• Use of fish oil supplements in people with no known CVD were associated with increased risk of stroke and atrial fibrillation.
• Risk of major adverse cardiovascular events was greater in women (hazard ratio 1.06, 95% CI 1.00 to 1.11, P value for interaction=0.0055) and non-smokers (1.06, 1.06 to 1.11, p=0.001).
• Regular use of fish oil supplements in people with diagnosed CVD was associated with a decreased risk of disease progression.
• The protective effect was greater in men (hazard ratio 0.93, 95% CI 0.89 to 0.98, P value for interaction=0.003) and older participants >65 (0.91, 0.86 to 0.96, p=0.002).

Conclusion

This study found associations between the use of fish oil supplements and an increased risk of atrial fibrillation and stroke. Conversely, a beneficial association was reported against the progression of CVD. It is not currently known why fish oil supplements may have differential roles. Further studies are needed to confirm these results along with identification of the exact mechanisms. No causal relationships can be drawn due to the observational nature of this study.

• Adverse effects may be linked to doses or formulations. This data was not available in this study.
• This study provided information on potential associations and not causal relationships.
• Covariates including use of prescription drugs may modify the effects of fish oil supplementation.
• Due to the uncertainty around CVD, caution should be used around the use of fish oil supplements for primary prevention of CVD.
• In relation to disease progression, fish oil supplementation may have anti-hypertriglyceridemia and anti-inflammatory effects, improve endothelial function, and contribute to a reduction in thrombosis. However, the effects may vary dependent on use of statins.

• Observational studies provide information on potential associations only therefore further studies are needed to confirm any causal relationships and the exact mechanisms involved.
• Inconsistent results and conflicting findings between the results in this and other large studies may be due to differing dose and formulations.
• Results were based on hospital inpatient data and may be subject to additional confounding factors. In this study, 66.2% of participants were overweight or obese, 92.4% drank alcohol.
• A high proportion of the study population were white (94.2%) therefore the results may not be generalisable to other ethnic groups. Further studies are needed in a diverse range of populations.
• Future studies should also monitor behavioural changes over time.